Thanks Kellen & Anton, for your detailed explanation and links to advantages, appreciate it. changing my vote to *-0*, I suggest to show as warnings.
On Sat, Sep 29, 2018 at 8:06 PM Anton Chernov <mecher...@gmail.com> wrote: > And if you want a more authoritative opinion on that check out what the C++ > core guidelines are saying [1]: > > > ES.71: Prefer a range-for-statement to a for-statement when there is a > choice > > Reason > > Readability. Error prevention. Efficiency. > > Best regards > Anton > > [1] > > https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#Res-for-range > > > сб, 29 сент. 2018 г. в 16:13, Anton Chernov <mecher...@gmail.com>: > > > +1 > > > > Maybe it's not necessary to enforce usage of range-based for, but I would > > highly encourage to to it due to already named advantages. If code would > be > > introduced using the old-style there could be a comment suggesting the > new > > way. But why do the manual work and not leave that to the automated tool? > > > > And since it's already automated - wouldn't it be better to keep a > unified > > modern style? > > > > Just to make this a trend - C++ evolves quickly and this will not be only > > upgrade that would needed to be made. And the easier such upgrades get > > accepted the easier in general is to upgrade the codebase. > > > > Soon the standard will get ranges and concepts and this will change the > > way C++ applications get written significantly. It is a good habit to be > > open for changes and keep up with the trends. By using the new > > possibilities the language can offer you prepare yourself for further > > changes and are more likely to accept them, evolving your programming > style. > > > > Take a look at a new examples on modern usages (taken from [1]): > > > > // since C++17 > > for (auto&& [first,second] : mymap) { > > // use first and second > > } > > > > // since C++20 > > for (auto& x : foo().items()) { /* .. */ } // undefined behavior if foo() > > returns by value > > for (T thing = foo(); auto& x : thing.items()) { /* ... */ } // OK > > > > // since C++11 > > struct cow_string { /* ... */ }; > > // a copy-on-write string cow_string str = /* ... */; > > // for(auto x : str) { /* ... */ } // may cause deep copy > > for(auto x : std::as_const(str)) { /* ... */ } > > > > Regarding performance: it's really easy to prove that generated assembly > > is not changing at all. There is a really handy tool for that [2]. You > can > > check online the assembly for different language constructs and different > > compilers. > > > > Best regards, > > Anton > > > > [1] https://en.cppreference.com/w/cpp/language/range-for > > [2] https://gcc.godbolt.org > > > > сб, 29 сент. 2018 г. в 13:15, kellen sunderland < > > kellen.sunderl...@gmail.com>: > > > >> It's more readable because it's concise and it's consistent for many > types > >> you're looping over (i.e. primitive arrays, stl iterators, etc all work > >> the > >> same way). It's also useful because it's consistent with other > >> programming > >> languages, making C++ codebases much easier to read for novice and > >> intermediate developers. IMO it also leads to better naming in loop > >> bodies > >> as the concise style means you're less likely to have important 1 letter > >> variable names describing loop elements (e.g. no int i =0 or it ...). > >> More > >> motivation can be found in the cpp standards proposals for C++11 > >> http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1868.html and > >> http://open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3853.htm. > >> > >> > >> > >> On Sat, Sep 29, 2018 at 6:38 PM Naveen Swamy <mnnav...@gmail.com> > wrote: > >> > >> > Kellen, > >> > > >> > Could you please explain why you think range loops are better and how > it > >> > improves readability? this is a relatively new feature, many of them > >> are > >> > used to the old syntax, shouldn't we leave it for the developers to > >> choose > >> > the one that best suits the need and their familiarity. > >> > In general I support the notion of standardizing where necessary, > >> enforcing > >> > rules on loops seems little bit like micro-managing how you should > write > >> > C++ code for MXNet. > >> > > >> > -1(open to change based on new information) > >> > > >> > > >> > > >> > On Fri, Sep 28, 2018 at 5:20 PM Chris Olivier <cjolivie...@gmail.com> > >> > wrote: > >> > > >> > > ok then, my vote is still -1, however, because it’s just adding > >> needless > >> > > friction for developers imho. > >> > > > >> > > On Fri, Sep 28, 2018 at 7:42 AM kellen sunderland < > >> > > kellen.sunderl...@gmail.com> wrote: > >> > > > >> > > > "Range loops aren’t always the most performant way" Do you have an > >> > > example > >> > > > where there's a perf difference? > >> > > > > >> > > > "In addition, sometimes you want the index. Or maybe you want to > >> > iterate > >> > > > backwards, or not start from the first, etc. Maybe you want the > >> > iterator > >> > > > because you remove it from the list at the bottom of the loop.... > >> Seems > >> > > > like a rule for the sake of having a rule." > >> > > > > >> > > > I should have been more clear about this point. If you're using > the > >> > > index > >> > > > in the loop, doing reverse iteration, or not iterating from > >> > start-to-end > >> > > > this inspection is smart enough to realize it and will not suggest > >> > > > optimizing that type of loop. The loops that would be changes are > >> > _only_ > >> > > > the loops which are detected as equivalent to range-loops. > Examples > >> > can > >> > > be > >> > > > found here: > >> > > > > >> > > > >> > > >> > https://clang.llvm.org/extra/clang-tidy/checks/modernize-loop-convert.html > >> > > > or you can look at what's been changed in the ref PR. I've > >> initially > >> > set > >> > > > our confidence level at 'reasonable' but we could also set to > 'safe' > >> > > which > >> > > > would further reduce the number of loops the check would apply to. > >> > > > > >> > > > -Kellen > >> > > > > >> > > > On Fri, Sep 28, 2018 at 3:54 PM Chris Olivier < > >> cjolivie...@apache.org> > >> > > > wrote: > >> > > > > >> > > > > -1 > >> > > > > > >> > > > > Range loops aren’t always the most performant way. In addition, > >> > > sometimes > >> > > > > you want the index. Or maybe you want to iterate backwards, or > not > >> > > start > >> > > > > from the first, etc. Maybe you want the iterator because you > >> remove > >> > it > >> > > > from > >> > > > > the list at the bottom of the loop.... Seems like a rule for the > >> sake > >> > > of > >> > > > > having a rule. > >> > > > > > >> > > > > On Fri, Sep 28, 2018 at 2:12 AM kellen sunderland < > >> > > > > kellen.sunderl...@gmail.com> wrote: > >> > > > > > >> > > > > > Hello MXNet devs, > >> > > > > > > >> > > > > > I'd like to discuss uniformly adopting C++11 range loops in > the > >> > MXNet > >> > > > > > project. The benefits I see are: > >> > > > > > > >> > > > > > * Improved C++ readability (examples below). > >> > > > > > * Consistency with other languages. The range-loops are > quite > >> > > similar > >> > > > > to > >> > > > > > loops almost all other programming languages. Given we're a > >> > project > >> > > > that > >> > > > > > supports many languages this language consistency could be > >> positive > >> > > for > >> > > > > our > >> > > > > > community. > >> > > > > > * Consistency within the same project. Currently different > >> authors > >> > > > have > >> > > > > > different loops styles which hurts codebase readability. > >> > > > > > * Best available performance. There are often multiple ways > to > >> > > write > >> > > > > > loops in C++ with subtle differences in performance and memory > >> > usage > >> > > > > > between loop methods. Using range-loops ensures we get the > best > >> > > > possible > >> > > > > > perf using an intuitive loop pattern. > >> > > > > > * Slightly lower chance for bugs / OOB accesses when dealing > >> with > >> > > > > indexing > >> > > > > > in an array for example. > >> > > > > > > >> > > > > > If we decide to enable this uniformly throughout the project > we > >> can > >> > > > > enable > >> > > > > > this policy with a simple clang-tidy configuration change. > >> There > >> > > would > >> > > > > be > >> > > > > > no need for reviewers to have to manually provide feedback > when > >> > > someone > >> > > > > > uses an older C++ loops style. > >> > > > > > > >> > > > > > -Kellen > >> > > > > > > >> > > > > > Reference PR: > >> > https://github.com/apache/incubator-mxnet/pull/12356/ > >> > > > > > Previous clang-tidy discussion on the list: > >> > > > > > > >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > https://lists.apache.org/thread.html/b0ae5a9df5dfe0d9074cb2ebe432264db4fa2175b89fa43a5f6e36be@%3Cdev.mxnet.apache.org%3E > >> > > > > > > >> > > > > > ------------------------- > >> > > > > > Examples: > >> > > > > > for (auto axis_iter = param.axis.begin() ; axis_iter!= > >> > > > param.axis.end(); > >> > > > > > ++axis_iter) { > >> > > > > > CHECK_LT(*axis_iter, static_cast<int>(ishape.ndim())); > >> > > > > > stride_[reverse_index] = ishape[*axis_iter]; > >> > > > > > ... > >> > > > > > --> > >> > > > > > for (int axis : param.axis) { > >> > > > > > CHECK_LT(axis, static_cast<int>(ishape.ndim())); > >> > > > > > stride_[reverse_index] = ishape[axis]; > >> > > > > > ... > >> > > > > > -------------------------- > >> > > > > > for (size_t i = 0; i < in_array.size(); i++) { > >> > > > > > auto &nd = in_array[i]; > >> > > > > > pre_temp_buf_.emplace_back(nd.shape(), nd.ctx(), true, > >> > > nd.dtype()); > >> > > > > > } > >> > > > > > --> > >> > > > > > for (auto & nd : in_array) { > >> > > > > > pre_temp_buf_.emplace_back(nd.shape(), nd.ctx(), true, > >> > > nd.dtype()); > >> > > > > > } > >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > > >
